Wireless revolution could spell end of plugs

Batteries and sockets could become a thing of the past after scientists devised a way of recharging mobile phones and laptops without the need for cables.

Electrical engineers used mainly magnetic waves to operate a light bulb from a power source seven feet away.

They envisage a future in which portable electronic gadgets and even robots are capable of charging themselves without ever being plugged in. Dispensing with their bulky batteries would also help free society of the waste problem caused by battery disposal.

Although concerns have been raised about a possible link between electromagnetic waves and cancer, scientists believe the technology can be developed without posing any additional risks.

A team from the Massachusetts Institute of Technology which reports its feat today in Science Express, an online advance publication of the journal Science, refers to its concept as "WiTricity" (as in wireless electricity).

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Scientists and engineers have known for many years that transferring electric power does not require wires.

In this case, studies by the team at MIT’s Department of Physics, Department of Electrical Engineering and Computer Science, and Institute for Soldier Nanotechnologies exploited an effect closer to inductance, rather than radio broadcasts, where energy is picked up with an antenna in the latter.

Inductance is at work in transformers used to charge everyday appliances which contain coils that transmit energy to each other by the phenomenon of electromagnetic induction.

But transferring energy this way over distances more than a few inches is typically inefficient, with one famous early 20th century attempt by the pioneering electrical engineer Nikola Tesla using huge coils to transfer a tiny amount of energy.

It can also be dangerous, with current concerns focusing on a possible link between some kinds of electromagnetic radiation and leukaemias.

However, Prof Marin Soljacic realised that instead of irradiating the environment with electromagnetic waves, a power transmitter could fill the space around it with a "non-radiative" electromagnetic field.

Energy would only be picked up by gadgets specially designed to "resonate"with the field, though working out the details was not easy, requiring theoretical calculations and computer simulations.

When asked whether it would pose theoretical risks, he told The Daily Telegraph that "it should be possible to make such a scheme operate within regulatory safety standards for general population exposure."

In this way, the team was able to light a 60W light bulb from a power source seven feet away; there was no physical connection between the source and the appliance, each of which contains a copper coil.

The team calculates that an object the size of a laptop could be recharged within a few metres of a wireless power source.

Wireless, he said, could also power other household gadgets that are now becoming more common.

"At home, I have one of those robotic vacuum cleaners that clean your floors automatically," Prof Soljacic said. "It does a fantastic job but, after it cleans one or two rooms, the battery dies."

If all portable devices could scavenge energy from the radio waves that surround us then maybe the battery charger could become a thing of the past.

However, someone, somewhere and somehow still has to generate that energy in the first place and the real technical question in this ever environmentally concerned world is whether energy distribution by radio is really as efficient as taking it from the electrical power distribution network through a charger.

The Massachusetts Institute of Technology team behind the project consists of Andre Kurs, Aristeidis Karalis, Robert Moffatt, Prof. Peter Fisher, and Prof. John Joannopoulos, led by Prof. Marin Soljacic.